1. Field of the Invention
The present invention relates to a tape traveling apparatus for travelling a magnetic tape while keeping constant the tension of the magnetic tape in a signal recording and playing back apparatus such as an audio tape recorder and video tape recorder (VTR), which uses the magnetic tape as a recording medium.
2. Description of Prior Art
For example, the tape traveling apparatus of a VTR has a tension control function for controlling the tension of a magnetic tape in order to reduce the gap loss for recording and playing back by pressing the magnetic tape against a rotating magnetic head with a proper pressing force and to reduce the jitter of signal to be played back by alleviating tape tension variation.
A control has previously been performed to keep the tension of a magnetic tape at a proper value by installing a tension detector for detecting the tension of the magnetic tape and by controlling the driving torque of a supply reel on which the magnetic tape is wound according to the detected result. Such control is disclosed in, for example, "Latest Technical Data Collection for VTR Design" (issued from Japan Industrial Technology Center, the first edition, 1987).
According to the above control method, however, a feedback control system to tension variation is constructed, so that a phase lag element depending on the control band exits. Thus, a problem develops that a sufficient inhibition effect for dynamically controlling the position of a magnetic tape cannot be obtained in order that a magnetic head scans correctly the recording track on the magnetic tape. In this case, an increased control gain of tension control can solve this problem. However, another problem still exists that there is usually a mechanical looseness between the supply reel and the driving mechanism for driving the supply reel such as for a casettee tape VTR, and an increased control gain causes a backlash to develop due to the looseness, with the result that the control gain cannot be sufficiently secured.